Omnidirectional slot antenna for mounting on cylindrical space vehicle

ABSTRACT

An extremely thin microwave array antenna which is bonded, circumferentially to the outside surface of a spacecraft and coated with a dielectric for thermal protection. This antenna was designed for a specific payload application in the S-band (2,200 to 2,300 MHz.) frequency range and provides an omnidirectional radiation pattern in the plane of the array and a nearomnidirectional pattern in the planes perpendicular to the array.

United States Patent Campbell et a1.

[451 Mar. 28, 1972 Meredith W. Appleton, Yorktown, both of Va.

[73] Assignee: The United States of America as represented by theAdministrator of the National Aeronautics and Space Administration [22]Filed: Sept. 18, 1970 [21] Appl.No.: 73,310

[52] US. Cl ..343/708, 343/771, 343/873 [51] Int. Cl. ..H0lq 13/10 [58]Field of Search ..343/705, 708, DIG. 2, 769,

[56] References Cited UNITED STATES PATENTS 3,518,685 6/1970 Jones..343/77l 3,569,973 3/1971 Brumbaugh et a1 ..343/771 PrimaryExaminer-Eli Lieberman Attorney-Howard J. Osborn, William H. King andJohn R. Manning [57] ABSTRACT An extremely thin microwave array antennawhich is bonded, circumferentially to the outside surface of aspacecraft and coated with a dielectric for thermal protection. Thisantenna was designed for a specific payload application in the S-band(2,200 to 2,300 MHz.) frequency range and provides an omnidirectionalradiation pattern in the plane of the array and a near-omnidirectionalpattern in the planes perpendicular to the array.

9 Claims, 4 Drawing Figures noooooo g 2| 0 H o I? 2o' O IIOOOOOO 0 o.- ol7 8 l8 0 ----Q-J'o o 2| 8 00000 20 8 .g 3W9 81 8 0 i7 8 1000001 2o --gf0 so 0, I0 0000*- OMNIDIRECTIONAL SLOT ANTENNA FOR MOUNTING ONCYLINDRICAL SPACE VEHICLE ORIGIN or THE INVENTION The inventiondescribed herein was made by an employee of the United States Governmentand may be manufactured and used by or for the government withoutpayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates generally to antennasand more specifically concerns an extremely thin omnidirectionalmicrowave array antenna.

In the past, the standard telemetry frequencies for rocket launchedpayloads have been in the 220-260 MHz. range. Presently, however, themilitary and scientific requirements have causedthese frequencies tobecome less available, thereby causing most scientific telemetryapplications to shift to the higher frequencies of 2,200-2,300 MHz. Duetothe nature of the tracking problem at S-band frequencies and higher,omnidirectional radiation patterns are a stringent requirement for mostspacecraft antenna systems. Therefore, a major problem expected in theshift to the S-band frequencies in the designing of antenna arraysmounted on surfaces large in terms of a wavelength that will (1) providenearly omnidirectional patterns with a minimum fluctuation, (2) satisfythe structural requirements while arraying a large number of antennas,and (3) perform properly through expected spacecraft environments. It istherefore the primary purpose of this invention to provide an S-bandfrequency antenna array suitable for space-craft applications.

SUMMARY OF THE INVENTION The antenna array that constitutes thisinvention consists of circumferential slots fed by a stripline circuitthat is an integral part of the array. The array is formed by laminantsof copperclad dielectric material producing a total antenna thickness of0.094 inch. Due to the slight thickness of the array, it is bonded tothe outside surface of the spacecraft and then coated with a suitableablation material. All antennas are interconnected by way of thestripline circuit between the laminants and the array is fed byproviding a single hole through the spacecraft structure for aradio-frequency connector. This design is unlike a discrete array inwhich mounting holes, brackets, and structural doublers would berequired for each antenna as well as provisions for power-distributioncircuits. For a payload application tested, this array reduced theantenna weight considerably over that of a discrete source array,provided additional space inside the spacecraft for instrumentation, andprovided excellent antenna characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of the antennaarray that constitutes this invention;

FIG. 2 is the sectional view 2-2 in FIG. 1;

FIG. 3 is a schematic drawing of the stripline circuit used in theantenna array; and

FIG. 4 is a schematic drawing of the antenna array attached to theoutside surface of a spacecraft.

DETAILED DESCRIPTION OF THE INVENTION Turning now to the embodiment ofthe invention selected for illustration in the drawings, the number 11in FIGS. 1 and 2 designates the outside layer of the antenna whichconsists of a cylindrical sheet of copper-clad dielectric cloth havingan outside layer of copper l2 and an inside layer of dielectric material13. Located inside cloth 11 is another cylindrical sheet of copper-claddielectric cloth 14 having a layer of copper 15 and a layer ofdielectric material 16 which is against the layer of dielectric material13. Layer 12 has eight circumferential slots 17 cut through it. Astripline circuit 18 which is shown in FIG. 3 is located between cloths11 and 14 with the fingers 19 of the stripline circuit connected orsoldered to the slots 17. Cloths l1 and 14 have their dielectric sidesbonded together and their copper layers connected together by copperrivets 20 to form cavities 21 between the copper layers. A radiofrequency connector 22 extends through cloth l4 and is soldered to thestripline circuit 18 at feed point 23.

In FIG. 4, there is shown a cylindrical section 25 of a spacecraft withthe embodiment of the invention 26, as disclosed in the FIGS. 1-3,attached to the spacecraft and covered with a layer of ablation material27. The radio frequency connector 22 extends through the walls of thespacecraft to provide a single connection to the antenna.

The fabrication of an extremely thin array in accordance with thisinvention composed of eight circumferential slots will now be discussed.This antenna was fabricated for use on a cylindrical section of aspacecraft having a length of 6 inches and a diameter of 8.61 inches.Layers l1 and 14 were constructed from 2-oz. copper-clad dielectriccloth having a dielectric constant of 2.10 which is commerciallyavailable.

The dielectric layers were cutto the proper size and each layer wasrolled into a 9-inch diameter cylinder. This diameter allowed asufficient amount of overlap prior to cutting each layer to the exactcircumferential length. The inside layer was rolled or formed with thedielectric side on the outside and the copper surface inside. A buttjoint was formed with the inside layer by soldering a copper stripacross the joint on the copper side of the layer. The joint was laterfilled with an epoxy adhesive. Prior to rolling the outside layer, thelayer with the copper surface on the outside and the dielectric surfaceinside, the slots were formed by cutting away the copper surface.

The slots were made 2.4 X 0.10 inches which is slightly longer than the2.26 inch lengths specified by test results using a single-coated slot.It was believed that this additional length would compensate slightlyfor tolerance effects, and length could be easily shortened later afterpreliminary array measurements were concluded. The dimensions of eachcavity were also outlined prior to rolling the outside layer. Theoutline would be the rivet line and the rivets would be placed in afterthe two layers were bonded together. In order to obtain a smooth surfaceon both sides of the flight antenna, copper countersunk rivets were usedinstead of bolts. The outside layer was then rolled into a 9-inchdiameter cylinder.

The stripline circuit was bonded to the dielectric side of the outsidelayer, and the feed loops were then placed through holes 0.60 inch fromthe end of the slot. A hole 0.50 inch in diameter through the outsidelayer was provided at the feedpoint location. This hole would facilitatesoldering the stripline to the radio frequency connector later.

Since the inside layer was in the form of a cylinder but was not closeto 8.61 inches in diameter, a 0.125 inch diameter hole for the feedconnector was drilled 0.5 inches from one edge of the layer. Theconnector would be placed there later. The outside layer, also being inthe form of a cylinder, was positioned so that the stripline feed wouldaline properly with the connector hole on the inside layer. The layerswere then bonded together and a copper strap was soldered across thejoint on the outside surface. Both dielectric surfaces were chemicallytreated to facilitate bonding. After the bond was sufficiently cured,pilot holes were drilled along the rivet line on the outside surface andcopper countersunk rivets were then placed in the holes approximately0.30 inch apart. These rivets thereby formed the individual cavities forthe slots as well as for the rectangular transmission line. Thecountersunk rivets were placed through the two layers and peened over onthe inside to form a fairly smooth surface inside and outside. Theantenna was then ready to be bonded to the payload cylindrical section.

Since the antenna had been rolled to a slightly larger diameter it couldslide over one end of the cylinder. A hole large enough to accommodatethe feed connector had already been drilled in the payload cylinder. Theantenna was then bonded to the payload cylinder under a vacuum toeliminate air bubbles in the epoxy adhesive. After bonding the feedconnector was soldered in place on the inside antenna surface, and thehole in the outside surface provided a means of soldering the strip-linecircuit to the center conductor of the feed connector. A patch ofcopper-clad dielectric material was placed in the outside hole andsoldered securely in place. The feed lines for the individual slots werethen soldered in place and the array was ready for testing. Aftertesting, indicated adjustments were made to the slots. Then the arraywas ready for coating with a heat-protective ablation material.

The advantages of this invention are numerous. It provides an antennaarray which provides an omnidirectional radiation pattern in the planeof the array and a near-omnidirectional pattern in the planesperpendicular to the array for S-band applications. It is extremelylight and requires very little space on the spacecraft. It is fed byproviding a single hole through the spacecraft structure for a radiofrequency connector.

It is to be understood that the form of the inventionherewith shown anddescribed is to be taken as a preferred embodiment. Various changes maybe made in the shape, size and arrangement of parts. For example,equivalent elements may be substituted for those illustrated anddescribed herein, parts may be reversed and certain features of theinvention may be utilized independently from the use of other features,all without departing from the spirit or scope of the invention asdefined in the subjoined claims. The embodiment of the inventiondisclosed shows an array of eight antennas. However, many more or manyless than eight could be used without departing from this invention.Also the embodiment is shown in a cylindrical form; whereas other shapesof the array could be made without departing from the invention. Forexample, the array could be put on a flat surface and instead of havinga plurality ofantennas only one could be used.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A microwave array antenna comprising:

first and second sheets of material with each including a' layer ofelectrically conducting material and a layer of electricallynonconducting material;

said first and second sheets placed together such that theirnonconducting layers are together;

a plurality of slots cut into said layer of electrically conductingmaterial of said first sheet;

circuit means connected to each of said slots and extending through saidsecond sheet; and

electrically conducting means connecting the electrically conductingmaterial layers of said first and second sheets together around each ofsaid slots to form a cavity back of each of said slots whereby aplurality of microwave antennas are formed which can be fed by a singlesource.

2. A microwave array antenna according to claim 1 wherein said first andsecond sheets of material are sheets of copperclad dielectric cloth.

3. A microwave array antenna according to claim 1 wherein said circuitmeans includes a stripline circuit.

4. A microwave array antenna according to claim 1 wherein saidelectrically conducting means are copper rivets.

5. A microwave array antenna according to claim 1 where two sides ofsaid first and second sheets are attached together to form a cylinderwith said first sheet on the outside of said cylinder, with said secondsheet on the inside of said cylinder and with said slots on acircumference of said cylinder whereby said antenna will produce anomnidirectional radiation pattern.

6. A microwave array antenna according to claim 5 wherein the inside ofsaid cylinder is attached to a cylindrical section of a spacecraft andsaid circuit means extends through the wall of said spacecraft.

7. A microwave array antenna according to claim 6 with the outside ofsaid cylinder coated with an ablation material.

8. A microwave antenna comprising:

first and second sheets of material with each including a layer ofelectrically conducting material and a layer of electricallynonconducting material; said first an second sheets placed together suchthat their nonconducting layers are together;

a slot cut into said layer of electrically conducting material of saidfirst sheet;

circuit means connected to said slot and extending through said secondsheet; and

electrically conducting means connecting the electrically conductingmaterial layers of said first and second sheets together around saidslot whereby a cavity-backed slot antenna is formed.

1 A microwave antenna according to claim 8 wherein said first and secondsheets of material are sheets of copper-clad dielectric cloth.

i k II

1. A microwave array antenna comprising: first and second sheets ofmaterial with each including a layer of electrically conducting materialand a layer of electrically nonconducting material; said first andsecond sheets placed together such that their nonconducting layers aretogether; a plurality of slots cut into said layer of electricallyconducting material of said first sheet; circuit means connected to eachof said slots and extending through said second sheet; and electricallyconducting means connecting the electrically conducting material layersof said first and second sheets together around each of said slots toform a cavity back of each of said sLots whereby a plurality ofmicrowave antennas are formed which can be fed by a single source.
 2. Amicrowave array antenna according to claim 1 wherein said first andsecond sheets of material are sheets of copper-clad dielectric cloth. 3.A microwave array antenna according to claim 1 wherein said circuitmeans includes a stripline circuit.
 4. A microwave array antennaaccording to claim 1 wherein said electrically conducting means arecopper rivets.
 5. A microwave array antenna according to claim 1 wheretwo sides of said first and second sheets are attached together to forma cylinder with said first sheet on the outside of said cylinder, withsaid second sheet on the inside of said cylinder and with said slots ona circumference of said cylinder whereby said antenna will produce anomnidirectional radiation pattern.
 6. A microwave array antennaaccording to claim 5 wherein the inside of said cylinder is attached toa cylindrical section of a spacecraft and said circuit means extendsthrough the wall of said spacecraft.
 7. A microwave array antennaaccording to claim 6 with the outside of said cylinder coated with anablation material.
 8. A microwave antenna comprising: first and secondsheets of material with each including a layer of electricallyconducting material and a layer of electrically nonconducting material;said first and second sheets placed together such that theirnonconducting layers are together; a slot cut into said layer ofelectrically conducting material of said first sheet; circuit meansconnected to said slot and extending through said second sheet; andelectrically conducting means connecting the electrically conductingmaterial layers of said first and second sheets together around saidslot whereby a cavity-backed slot antenna is formed.
 9. A microwaveantenna according to claim 8 wherein said first and second sheets ofmaterial are sheets of copper-clad dielectric cloth.